The invention relates to a detector arrangement in connection with a mobile work machine.
The invention further relates to a method of determining a mutual position or a mutual state of motion of at least two structural parts of a mobile work machine.
Determination of an absolute or a relative position of structural parts of mobile work machines, such as forest work units, is necessary e.g. for controlling the machines, improving the operator's work ergonomics, ensuring safe and efficient working, and managing forces to which the machine is subjected. Various solutions are known for determining the position of the structural parts. These solutions are often based on contact and/or mechanical connection, such as articulation angle measurements between two structural parts by means of a rotation angle sensor to be installed directly in a joint, such as a resolver, or, alternatively, e.g. measurements of a position of linear movement of a linear actuator controlling a rotating joint by means of resolvers or potentiometers, for instance. However, all known solutions present problems that are usually caused by the measuring methods and devices used as well as the operating manners and operating conditions of the forest work units and/or the compatibility thereof. Forest work units are, for instance, used in a varying, often slanting and rough terrain, they are subjected to mechanical impacts e.g. by branches, trunks and stumps as well as to various kinds of vibration, booms and loads arranged thereon apply forces and strains to the machines. In addition, environmental conditions, such as great variation in outside temperature as well as moisture and impurities, may harm sensors arranged particularly in connection with the structures of a forest machine or control electronics of the machine.
Determination of an angular position by using different conventional inclination detectors presents various problems. A problem with detectors based on an acceleration sensor is that other accelerations, in addition to gravitational acceleration, directed at the sensor cause distortion in an angular value. Therefore, it is usually necessary to filter a signal heavily in order to reduce these distortions, which, in turn, makes the filtered signal slower to react to changes in the angle. Detectors based on detecting angular velocity, such as gyroscope measuring devices, in turn, detect the rate of change in the angle rather than the absolute position in relation to the direction of an acceleration due to gravity vector, for instance. Consequently, errors caused by non-idealities of the measurement and measuring arrangements accumulate during use in the angular position determination based on angular velocity.